15.2.1 Introduction to the Island Perforator Flap

Just what is a “true” island perforator flap (Fig. 15.2) is a highly controversial idea. Theodore Dunham ¹ (1892) is credited with using the term clinically for the first time, and he defined an island flap as one having an axial pedicle that is skeletonized and then tunneled under a cutaneous bridge to allow coverage of a nonadjacent defect. Today the term has become less specific, often applied to any flap whose peripheral boundaries are separated in toto from its donor site, ^{2 ,​ 3} remaining attached only by whatever is its source of vascularization. For example, a V-Y or keystone “island” advancement flap remains attached only by a broad base to the underlying deep fascia. ⁴ A propeller perforator flap is connected only at its hub, that typically being a single perforator that at most has been dissected back to its source vessel to form what is often called an island flap. Rather than an “island” flap, which is somewhat of a misnomer, a better term for the latter two examples might be “islanded” flaps.

Yet Dunham’s ¹ definition still has merit for describing this subtype of lower limb local perforator flaps. What is a “true” island perforator flap must be approached somewhat differently in order to obtain its somewhat unique attributes. Not only must all skin margins be disconnected at the donor site, but also the axial pedicle providing the flap circulation must be extended beyond just the requisite diminutive perforator to include a major branch if not the source vessel itself. Early examples obeying Dunham’s ¹ definition in the lower leg were fasciocutaneous flaps that indeed were sustained by perforators from the anterior tibial, ⁵ posterior tibial, ⁶ or peroneal ^{7 ,​ 8} vessels, but these source vessels themselves were also elevated with the flap over considerable distances. For foot and ankle defects, usually these major vessels would be divided just proximal to the connected perforator-based flap, then the source vessel pedicle dissected distal to the desired point of rotation that allowed appropriate flap insetting. Reverse flow was essential for flap survival, and the source vessel itself was sacrificed irrespective of any risks of long-term sequela. The omnipresence of peripheral vascular disease would make this option unacceptable today, and fortunately many of the other perforator local flap subtypes can now provide the same benefit.

Nevertheless, from a practical standpoint, several possibilities for “true” island flaps still exist in the lower extremity. Zheng et al ⁹ have described use of a constant perforator of the descending genicular artery (DCA) to sustain a distal anteromedial thigh flap as a propeller flap, but this could also be an island flap for proximal thigh transposition if based instead on the DCA itself. Agko and Chen (Chapter 15E: Medialis Pedis and Other Plantar Flaps) have discussed several local plantar flaps that can similarly be extended on the medial plantar artery as island flaps to allow reach to many sites about the foot and ankle. However, two more pragmatic options in the lower limb are island anterolateral thigh (ALT) and medial sural artery perforator (MSAP) flaps. As is well known, the proximal-pedicled ALT island flap can reach superiorly to the lower abdomen, laterally the greater trochanter, and medially the perineum (Fig. 15‑3). ^{10 ,​ 11} Both a distal-pedicled ALT island flap (Fig. 15‑3) ¹² and a proximal-pedicled MSAP island flap ¹³ (Fig. 15‑4) can cover the patella or the proximal lower leg. Because these “true” island flaps rely on inclusion of their source vessel, the descending branch of the lateral circumflex femoral (LCF) or medial sural artery, respectively, reach of these flaps is limited only by the potential length of that pedicle.

15.2.2 Attributes and Detriments

15.2.3 Anatomical Considerations

To avoid redundancy, the basic anatomy of the ALT and MSAP flaps is no different than as catalogued in Chapter 16. As a local island flap, however, the difference will be the need to extend the source vessel pedicle while always being retained in situ at the point of flap rotation. For example, the pedicle of the MSAP flap can be lengthened to improve reach by dissection back to its origin from the popliteal vessels. The ALT flap pedicle similarly can be freed up back to the LCF vessels. Once this maneuver has been accomplished, passing the island ALT flap under the rectus femoris muscle will further increase reach to the midline or beyond. ¹⁴ If the ALT flap is used as a distal-based flap, maintenance of communications of the descending branch of the LCF system, which presumably also services the flap perforator, with collaterals from the lateral superior geniculate vessels for reverse flow will be essential. ¹²

15.2.4 Anatomical Variations and Potential Pitfalls

15.2.5 Flap Design

Design of the ALT or MSAP island flaps will be identical as outlined in Chapter 16 when used as a free flap. Eccentric placement of the skin boundaries as distal to the chosen perforator as possible will allow the longest possible pedicle to extend reach as a local island flap.

15.2.6 Flap Harvest

The elevation of a proximal-pedicled MSAP (Fig. 15‑4; see Video 15.1) or ALT (Fig. 15‑5; Video 15.2; and also see Chapter 16: ALT subchapter, Fig. 16.3; see Video : ALT island flap harvest) island flap will be no different than as described if used as a free flap (see Chapter 16) with patient positioning being also the same, except that the pedicle must be dissected as far proximally as necessary to obtain the required reach. Maximally, this would be the popliteal artery for the MSAP island flap or the LCF artery for the ALT island flap. A distal-pedicled ALT flap should still have the same dissection of its proximal pedicle. ¹² This will not only allow potential supercharging whether arterial or venous, but also confirm that the flap perforator arises from a vessel in some way connected to the distal portion of the descending branch of the LCF, which will then still provide reversed flow to sustain the flap. Distal dissection of this pedicle into the vastus lateralis muscle must be enough so that reach to the defect is possible, but at the same time maintaining vessels of reasonable caliber to ensure collateralization with the lateral superior geniculate vessels. After insetting the flap, Lin et al ¹² recommend venous supercharging in all cases with an end-to-end microanastomosis of the largest vena comitantes of the proximal ALT pedicle to the greater saphenous vein that can be brought to the flap from the medial leg.

15.2.7 Postoperative Care Protocols

The potential for compression not just of the vascular pedicle to these island flaps that are usually passed through a subcutaneous or submuscular tunnel, but also the diminutive perforators themselves requires that the flaps be observed as carefully as per the usual protocol for a free flap. If the flap crosses a joint, immobilization is essential to prevent movement resulting in stretching of the pedicle, its obstruction or disruption, or even flap dehiscence.

15.2.8 Conclusion

A “true” island perforator flap not only will have all its skin boundaries disconnected from those of its donor site but also will have an elongated pedicle extending beyond just the flap perforator itself, or else would more properly be called an “islanded” flap. This will therefore require inclusion of a major branch or the source vessel of the perforator itself as part of the flap pedicle. Previously, this has been accomplished by sacrificing either the anterior tibial, ⁵ posterior tibial, ⁶ or peroneal ⁷ artery, but this is no longer an acceptable risk under any conditions for fear of eventual devascularization or ischemia of the foot. Other more straightforward local perforator flap alternatives today have become superior options. ¹⁶ However, the territories of the ALT or MSAP flaps still represent pragmatic choices for island flaps that as such have far greater reach for coverage of proximal or distal defects of the lower limb than do other local perforator flap subtypes.

15.3.1 Introduction to the Perforator Advancement Flaps Including the Keystone Flap

An advancement flap by definition is always moved in a forward direction into a defect without any rotation or lateral movement. ¹ A classic prototype was a unipedicled quadrilateral-shaped random flap sustained by a skin bridge on one side that is now primarily only of historical interest as this geometric arrangement has limited mobility and therefore inadequate reach in the lower extremity. ¹ The advent of the perforator flap concept provided an improved means for advancement flap vascularization, but practically has been limited in the lower extremity to V-Y advancement and keystone island flap designs.

According to Niranjan et al, ² Blasius (1848) should be credited with the idea of the V-Y advancement flap, which for a long time was based on a subcutaneous pedicle ³ with reach dependent on the sliding capability of these triangular shaped skin flaps. ^{4 ,​ 5} Since in actuality the fascial plexus alone within the subcutaneous tissues can be quite tenuous, these flaps more likely have always received their circulation from unrecognized perforators of the deep fascia and fascia feeders surrounding it. ² The same comments also apply to the recent variation introduced by Behan ⁶ as the “keystone design perforator island flap (Fig. 15.6).” This basically is a trapezoidal islanded flap ⁷ that consists of two conjoined ^{7 ,​ 8} or opposed ⁹ V-Y advancement flaps. Although usually stated to be islanded, the keystone flap still maintains some connection to the deep fascia directly underneath it. In contradistinction, additional reach no longer relying on skin laxity of a V-Y advancement flap is possible if the flap can be isolated on a distinct perforator, ^{2 ,​ 7 ,​ 10 ,​ 11} whereas the multiple perforators to a keystone flap are never specifically sought out. ¹²

15.3.2 Attributes and Detriments

15.3.3 Anatomical Considerations

Neither a V-Y advancement flap nor a keystone flap absolutely requires identification of a specific perforator. Both can be supplied by perforators of the deep fascia, which could be no more than the ubiquitous capillary perforator, ¹³ or fascia feeders. ² As such, these flaps should be oriented to overlie known perforators or areas of high perforator density, that is, “hot spots,” ¹² following the longitudinal course of the three source vessels to the foot. If a perforator can be precisely determined preoperatively using available adjunctive techniques, a V-Y advancement flap could instead become an islanded flap connected only to that specific perforator, which would thereby have farther reach, albeit still limited by the length of the perforator itself.

As with any local perforator flap, the condition of local tissues and possible compromise of perforators must always be assessed carefully. In addition, unique to the lower extremity, advancement flaps may be more difficult, ¹⁴ as tissue laxity or slipperiness may be nonexistent over the deep fascia although still probably adequate over the muscles of the thigh and calf, if anywhere. As a consequence, transverse oriented V-Y advancement flaps are more mobile, ^{5 ,​ 11} as would be longitudinally designed keystone flaps. ⁹ For keystone flaps, this is an advantage, as this best recruits circulation from multiple captured perforators perhaps from adjacent territories according to the perforasome theory. ¹⁵

15.3.4 Anatomical Variations and Potential Pitfalls

Extended Reach

Salvage of Intrinsic Flap Tissues

Rather than discarding the tissues of the margins of the leading edge of an advancement flap, these can be sewn together, thereby increasing the width of the flap and consequently lessening the amount of advancement needed. For the V-Y advancement flap, this maneuver has been called the PAC-Man technique ^{2 ,​ 16 ,​ 17} (Fig. 15‑7) and for the keystone flap, the omega technique ¹⁴ (Fig. 15‑8).

Deep Fascia Release

Often an incision of the deep fascia as needed about either the V-Y advancement or keystone flap will allow greater movement, as restraints from connections to the underlying tissues are partially released. Usually this begins at the greater curvature border of the keystone flap ^{9 ,​ 12} and progresses outward as required to obtain the desired flap mobility. Subfascial extension of this dissection to get even more release should best be away from areas of known high perforator density so they will not be injured.

Suprafascial Flap Release

Instead of incising the deep fascia and violating perforators and perhaps fascial feeders, a suprafascial dissection raising the subcutaneous tissues of either the V-Y advancement or keystone flap from the deep fascia as needed for further advancement can be done. This requires careful preservation of any small vessels encountered, which makes this a more difficult alternative as microdissection will be required. ¹⁸ The V-Y advancement flap should be elevated at its apex and base first, whereas for the keystone flap, margins should be explored where perforator density is known to be the least.

Rotation Advancement Flap

If an islanded V-Y advancement flap is intended, but during the subfascial dissection through the exploratory incision via one side of the flap no adequate perforator is found, the flap should be redesigned retaining the contralateral side intact. The base can then be advanced forward with some rotation about its intersection and the retained side to then close the defect ¹⁹ (Fig. 15‑9). This may require a small back-cut of the retained side starting at the flap apex to allow adequate rotation.

Keystone “Plus” Flap Design

A “V”-shaped extension half of the defect width is designed in the center of the greater curvature of the arc that connected the tangential wings of the standard keystone flap (Fig. 15‑10). ²⁰ After flap advancement, this donor site is also closed in a V-Y fashion, which should relieve tension on closure of the greater curvature side of the overall donor defect.

Keystone Flap Skin Bridge Design

The cutaneous central member of the greater arc of the keystone flap is not incised, although the deep fascia is released in its entirety underneath this skin bridge that has been left intact (Fig. 15‑11). This should not restrict closure of the donor site. Subdermal lymphatics from the flap are preserved, and Moncrieff et al ²¹ believe the flap will also have greater vascularity via this connection. However, this contradicts the opinion of Behan ^{14 ,​ 22} who believes that the creation of a completely islanded flap causes a sympathectomy effect that results in augmented, not diminished, flap perfusion.

15.3.5 Flap Design

V-Y Advancement

The laxity of tissues adjacent to the defect will determine the orientation or even possibility of using this option as a subcutaneous pedicled flap as the keystone flap is typically used. The base of the isosceles triangular shaped flap should slightly exceed the width of the defect (Fig. 15‑12). The altitude of the flap will extend perpendicular to the base up to 1.5 to 2.0 times the height of the defect, with a longer flap probably allowing easier closure of the donor site at the apex of the flap that will be in the vicinity of the most pliable donor site tissues.

If subcutaneous tissue elasticity is known to be inadequate for the needed advancement, preoperative search for a nearby perforator should be undertaken. If the perforator is close to the defect, a propeller flap may be a preferred option. ⁷ If the perforator is further from the defect, it may be more appropriate to design a V-Y advancement flap using the same dimensions as for the subcutaneous pedicled version, although now instead centered over the requisite perforator (Fig. 15‑13).

Keystone Flap

Behan classified keystone flaps into four types that varied by the degree of undermining of the deep fascia, number of flaps used, or treatment of the donor site, which rarely required a skin graft. ⁶ His standard format is a representative model of all his subtypes that will be the focus here (Fig. 15‑14). Although in the past many have extended the original defect in an elliptical fashion to coincide with the lesser curvature of the flap, ¹⁴ in the lower extremity this can be a waste of precious normal tissues that may instead require alteration of the flap design (Fig. 15‑15). ⁸ Local tissues about the defect should be assessed for the presence of perforators and compared to areas with maximum skin laxity. This can be facilitated by the use of an audible Doppler; however, knowledge of known high-density perforator locations, that is, “hot spots,” ¹² or the fact that perforators commonly emanate following the longitudinal course of the source vessels to the foot can be used safely with impunity. Since perforasomes in the lower extremity interconnect in a longitudinal direction, ¹⁵ the keystone flap should have a similar axis especially if the most pliable tissues can be simultaneously captured.

Wings starting tangential to the defect on opposite sides should proceed at about a 90-degree angle away for at least as far as the height of the defect. This distance determines the width of the keystone flap. The two tangent lines are joined by an arc to complete the trapezoidal or keystone shape of the flap. If the lesser curvature edge of the flap has already been undermined, its tissues are of poor quality such as irradiated, inelastic, or traumatized, the wings and thus the width of the flap can be increased even up to 5:1 the size of the defect so as to capture adequately perfused and elastic tissues having the desired qualities that can then be advanced as needed. ¹²

15.3.6 Flap Harvest

The position of the patient on the operating room table will depend on the location of the defect and the proposed design of the local perforator flap chosen for its correction, so as to most simply allow access to both.

15.3.7 Postoperative Care Protocols

Both the V-Y and keystone advancement flap versions pedicled by their deep fascial attachments are extremely robust flaps requiring little additional scrutiny as long as pressure is kept off them and adjacent joints relatively immobilized to minimize compression and stretch. On the contrary, an islanded V-Y advancement flap must be carefully protected so that the perforator itself will not be compromised, by appropriate dressings and positioning of the patient, for at least a week or more in most patients until wound healing stability is satisfactory. Sutures, especially in the keystone flap, should never be removed in a hurry, perhaps waiting several weeks or more sometimes so that dehiscence does not occur.

15.3.8 Conclusion

Local perforator advancement flaps basically allow only forward movement of tissues adjacent to a given defect. In the lower extremity, the most pragmatic variations are limited to the V-Y advancement or keystone flap. These on a geometric basis have great similarity in design, and also both can survive on multiple perforators through the deep fascia without the need for specific perforator identification. Yet in this form, both rely on tissue laxity to allow the required advancement, with the keystone flap concept necessitating at times even gigantic flaps if need be to obtain this reach. The V-Y advancement flap overall is limited to small or moderate-sized defects, where any additional reach if desired requires instead that a specific perforator be found so that an islanded version tethered only by the length of that as the vascular pedicle will prove to be sufficient.

15.4.1 Introduction to the Medialis Pedis and Other Plantar Flaps

The plantar aspect of the foot can serve as a source for several muscle, musculocutaneous, fasciocutaneous, or purely cutaneous flaps that can be transposed, rotated, or transferred as a free tissue flap. In terms of ankle and foot reconstruction, these flaps, due to their sizes and special features of the skin, are mainly used to cover small to moderate-size defects involving the plantar surface and hind foot (Fig. 15‑24).

Mir y Mir (1954) first used a random, cross-leg plantar arch flap transferred in three stages to cover heel defects on the contralateral foot. Later, Shanahan and Gingrass first described the pedicled medial plantar artery sensory flap from the ipsilateral foot based on the homonymous artery and nerve. ¹ Reiffel and McCarthy further refined the flap by narrowing its pedicle and suggesting a subfascial dissection. ² Harrison and Morgan reported the harvest of an island “instep flap” from the same area but including the underlying abductor hallucis muscle. ³ Morrison et al transferred this instep flap in a fasciocutaneous form (i.e., without the muscle) both as a pedicled island flap and as a free flap, extending its application to forefoot defects. ⁴ Finally, in 2001, Koshima et al introduced the free medial plantar artery perforator flap wherein a purely cutaneous instep flap is elevated based on a single perforator emanating through the intermuscular septum between the abductor hallucis and flexor digitorum brevis muscles. ⁵ This is where the superficial branch of the medial plantar artery, the pedicle of all the aforementioned flaps, is located. More recently, the medial plantar artery perforator flap has been successfully applied to defects involving all three weight-bearing regions of the sole: forefoot, midfoot, and heel. ^{6 ,​ 7}

Alternatively, the medial aspect of the midfoot can serve as a donor site for the distinct medialis pedis flap. In 1990, Masquelet and Romana demonstrated, both in cadaveric specimens and in clinical cases, the feasibility and reliability of this fasciocutaneous flap based on the medial (cutaneous) branch(es) that arise(s) from the deep branch of the medial plantar artery. ⁸ Due to the thin and thus pliable nature of the skin and size of this flap, it is particularly suitable for coverage for distal medial malleolus, distal Achilles tendon, and heel. Other less commonly used plantar flaps are the lateral plantar artery flap and various intrinsic muscle flaps that can be used to cover exposed structures and provide a reliable bed for skin grafting. ⁹

15.4.2 Medialis Pedis Flap

Anatomical Considerations

Despite numerous publications on the subject, there is considerable confusion in the literature as to the surgical anatomy of the medial plantar vessels. ¹⁰ While the division of the posterior tibial artery into the medial and lateral plantar vessels is not contested, the terminology for the subsequent branching of the medial plantar artery is much less uniform presumably reflecting the considerable anatomical variation. However, this should not dampen interest in these flaps, as irrespective of the specific branching pattern, there always is a reliable vessel that can nourish both the medialis pedis and the medial plantar artery flaps.

For the sake of simplicity, the predominant pattern will first be described and then the clinically relevant variations will be explored as appropriate. The posterior tibial artery divides into the medial and lateral plantar arteries at the posterior edge of the sustentaculum tali that corresponds to the lower edge of the flexor retinaculum. After coursing for 2.5 to 3.5 cm, the medial plantar artery further divides into its superficial and deep branches at the level of the talonavicular joint deep to the abductor hallucis muscle (Fig. 15‑25a). The superficial branch, which is the vascular source for the medial plantar (instep) flaps, proceeds distally in the intermuscular septum between the abductor hallucis and flexor digitorum brevis muscles (Fig. 15‑25b).

The deep branch remains deep to the abductor hallucis muscle and then divides into medial and lateral branches. The lateral branch dives deep in the foot to connect to the deep plantar arch. The medial branch courses over the tibialis posterior tendon (close to its insertion into the tubercle of the navicular bone) and wraps around the medial osseous arch. The cutaneous vessels from the medial branch (of the deep branch of the medial plantar artery) supply the medialis pedis flap (Fig. 15‑25b).

The tibial nerve is closely associated with the posterior tibial artery and in a similar fashion divides into medial and lateral plantar nerves. The medial plantar nerve accompanies the superficial branch of the medial plantar artery and provides sensation for the medial plantar flap. The sensory innervation of the medialis pedis flap on the contrary is provided by the saphenous nerve, which reaches the area as a continuation of the femoral nerve. The saphenous nerve can be included in the medialis pedis flap, yet reasonable protective sensation and moving two-point discrimination can be achieved even without coaptation of the nerve. ¹¹

A network of venae comitantes accompanies the medial plantar artery and its branches, and maintains the venous drainage of these flaps. Nevertheless, the superficial venous system should be included in the medialis pedis flap in case the deep venous system accompanying the arterial pedicle is diminutive and, therefore, inadequate.

Related posts:

3 Indications for Vascular Intervention in Lower Extremity Reconstruction 4 Orthopaedic Evaluation of the Lower Extremity and the Concept of the Orthoplastic Approach 10 General Wound Preparation and Timing 7 Using the Flap and Angiosome Concepts to Optimize Functional Lower Leg and Foot Amputations 17 Supermicrosurgery Approach to the Lower Limb 26 Perioperative Care and Rehabilitation Specific to the Lower Limb

Stay updated, free articles. Join our Telegram channel

Join